Large vehicles, such as diesel-electric locomotives and diesel-electric off-highway trucks, such as mining trucks, may be powered by electric traction motors. Electric traction motors for such vehicles may use an alternating current (AC) electric motor powered by either an alternating current alternator-rectifier or a direct current (DC) generator that in turn is powered by a diesel engine. Vehicles powered by such diesel-electric traction motors commonly use dynamic or rheostatic braking systems. In a dynamic braking system, the armature of each traction motor is connected across a forced-air-cooled resistance grid, known as a dynamic braking grid. In a diesel-electric locomotive, the dynamic braking grid typically is located behind the cab.
To brake a diesel-electric engine with a dynamic braking system, the electric traction motor is connected to function as an electric power generator that is driven by the rotating wheels of the moving vehicle. The electricity generated by the traction motor is conducted to the braking grid, which is a frame containing a resistance element in the form of thin metal plates connected in series. The metal plates are made of a material that is electrically conductive, but provides resistance to the current received from the traction motor so that the current is converted to heat that is radiated from the resistor elements. Diesel-electric engines usually employ multiple braking grids. Thus, the energy of motion of the locomotive engine, or other vehicle in which this configuration is installed, is converted to heat in the dynamic braking operation mode that is dissipated from the resistance element plates.
An issue that arises when dynamic braking systems are employed to brake a vehicle, such as a locomotive, traveling at high speed, or when the dynamic braking system is applied to a vehicle traveling downwardly on a relatively steep grade, is that the dynamic braking grid may overheat. Cooling fans typically are employed to direct ambient cooling air across the resistance elements of a dynamic braking grid to maintain the temperature of the resistance elements below a temperature at which damage to the resistance elements or other components of the braking system might occur.
The frame containing the plate-shaped resistance elements of dynamic braking grids typically is rectangular in shape, whereas the cooling fan utilizes a circular turbine to move air over the resistance elements. The circular turbine typically has a central circular hub and a plurality of radially extending fan blades. It is necessary to direct the air flow from the circular cooling fan evenly across the rectangular braking grid. If the air flow from the cooling fan flows unevenly over the resistance elements, hot spots that might occur on the resistor elements in areas with relatively low air flow. Cooling fans typically utilize a duct that encloses stationary vanes to direct air from the turbine of the cooling fan across the rectangular braking grid. Accordingly, there is a need for a cooling fan vane assembly for a resistor grid that effectively and efficiently distributes cooling air evenly across a resistor grid to dissipate heat generated by rheostatic braking.